An existing gas instantaneous water heater (as shown in FIG. 1) adopts a downward air-blasting blower 1′ to provide the air required for combustion, and the blower 1′ is mounted at the bottom of a combustion chamber. A combustion device 3 is arranged in the combustion chamber, and an air uniformizing board 6 is provided between an air outlet of the blower 1′ and the combustion device. Gas passes sequentially through a gas proportional valve 5 and the combustion device 3, and is in combustion at the top of the combustion device 3. The air provided by the blower 1′ passes sequentially through the blower 1′, the air uniformizing board 6 and the combustion device 3, and supports the combustion at the top of the combustion device 3. The air uniformizing board 6 sends out the air provided by the blower 1′ uniformly by passing through the whole air uniformizing board 6 via tiny through holes distributed thereon.
Researches show that the tiny through holes on the air uniformizing board 6 generates a relatively large resistance to the air provided by the blower 1′, which results in a relatively large pressure difference formed at the front and back of the air uniformizing board 6 and a relatively large pressure space formed between the air outlet of the blower 1′ and the air uniformizing board 6. In the case of same rotating speed, pressure P and air quantity Q at the air outlet of the blower 1′ are in an inversely proportional relationship (as shown in FIG. 2). In the case of same pressure at the air outlet of the blower 1′, air quantity Q of the blower 1′ is in direct proportion to rotating speed n of the blower (as shown in FIG. 3). Therefore it is required to improve the rotating speed of the blower 1′ to overcome the resistance at the air outlet of the blower 1′ so as to provide an amount of air required for combustion in the case of a relatively large pressure of the air outlet of the blower 1′ caused by the air uniformizing board 6. Theories and tests prove that the noise in operation of the blower 1′ is a main source of the noise of the gas instantaneous water heater, and the noise level is in direct proportion to square of the rotating speed. Therefore a downward air-blasting gas water heater produces relatively large noise during operation.
Chinese Utility Model patent Application No. 201020151828.4 discloses an updraught gas instantaneous water heater, wherein a heat exchanger is arranged on the upper part of the combustion device, a blower is arranged above the heat exchanger and provides an amount of air required for combustion for the combustion device by air draught. The inside of the combustion chamber is in a state of negative pressure all the time, and air flow field in the vicinity of the combustion device is relatively uniform with respect to that of a downward air-blasting structure. Therefore, there is no need to adjust the uniformity of the air by utilizing an air uniformizing board, thereby avoiding a high pressure area formed by the pressure difference caused by the adoption of the air uniformizing board. It can be seen from FIGS. 2 and 3 that a relatively low rotating speed of the blower could provide the amount of air for maintaining the combustion, thereby the noise generated during the operation of the heater could be suppressed.
However, in the updraught structure, the high temperature combustion flue gas (about 150 Celsius degree) is discharged by passing through an impeller of the blower, which has a relatively high requirement to heat resistance of the blower. The technical solution of the above patent can merely adopt a blower driven by an alternating current motor, for the reason that there is no need for a motor control panel, and the rest parts are all made of metal material which is capable of resisting high temperature up to 150 degree.
However, in the operation of the gas water heater, besides consideration of noise, it is also needed to regulate and control the blower according to actual combustion requirement to convey reasonable air amount, so as to sufficiently burn the gas while guarantee the required combustion temperature, so that the combustion is reliable and exhaust emission reaches the standard. An existing blower driven by the alternating current motor can rotate at only several limited numbers of rotating speed, therefore it is very difficult to achieve accurate control of the rotating speed of the blower and consequently popularization and application of the above patent technology is restricted.